Increment property value with keyboard
As @TeeTrinker said, you can left-click and drag the mouse to change the value in the field.  Of course, this will change the value by increments of 0.01.  If you want the value to change by increments of 1.0, you can hold down Ctrl while dragging:



An alternate way, purely by keyboard is to simply add 1.0 to the value in the field by typing + 1 and pressing Enter:



There may be other ways through scripts but I'm unsure.